1. Field of the Invention
The present invention relates to electrosensitive recording in which a metallic surface is electrically penetrated at designated locations to record information.
2. Description of the Prior Art
Electrosensitive recording materials typically have a base layer of paper that supports a resinous contrast coating on one side. A further coating of vapor-deposited metal, such as aluminum, covers the free surface of the resinous contrast coating. When electrical current is passed through a stylus or blade in contact with the metallized surface, the metal is vaporized along the path of contact of the stylus. This exposes the contrasting resinous layer, which prevents the vaporized metal from penetrating into the paper. The resinous coating also acts as a barrier to moisture vapor transmission and protects the paper base against chemical corrosion during the metal vaporization process. The resinous coating may include pigmentation such as carbon black. The resinous coating may further include additives, such as matting agents to reduce the gloss of the metallized surface, or pigments to provide a pronounced contrast to the metallic surface where the latter has been removed.
Contemporary printers for electrosensitive material have the disadvantage that print quality has not been as good as that obtained with competing printers. Another disadvantage has been the tendency to accumulate debris around the stylus, necessitating frequent shutdown of the printer for cleaning. Specifically, in the development of electrosensitive paper for use as a recording medium in computer output printers it heretofore has not been possible to produce a reasonably priced electrosensitive paper which could meet a large number of physical requirements, including, high tensile and tearing strength, high burst strength, good fingerprinting resistance, desired resistivity, favorable barrier properties, minimal structural curling, proper matte appearance, suitable print quality and limited production of debris during recording. It is also important that the electrosensitive paper not cause appreciable stylus wear.
Representative electrosensitive recording paper of the prior art employs a paper base layer covered by a contrast layer of a lacquer coating or printing ink, which in turn is covered by metallic aluminum. Illustrative U.S. Pat. Nos. of the prior art include 3,786,518; 3,831,179; 3,995,083; and 4,217,596.
In U.S. Pat. No. 3,831,179 an intermediate contrast layer of cellulose-based lacquer is used to produce corrosion resistance and has good barrier properties in that it prevents moisture vapor from being transmitted through to the paper base layer. This structure has the disadvantage that the contrast of the exposed resinous layer where the metallic surface is burned away is not satisfactory.
Numerous attempts have been made to improve the contrast between the recorded information and the outer metallic layer of the electrosensitive medium. Typically, carbon black pigment is added to the intermediate lacquer layer to produce a matting effect in an attempt to improve contrast. Such is the case in U.S. Pat. No. 3,995,083. Since carbon black is an electrical conductor, the amount which can be added is limited by the need to avoid current flow through the carbon black additive which can produce distortion of the intermediate layer by overheating.
In U.S. Pat. No. 3,786,518, an amorphous silicon oxide additive is added to enhance the matte properties of the intermediate lacquer layer. This is to improve the contrast between the recorded information and an aluminum coating. Although amorphous silicon oxide improves contrast, it also causes a rapid buildup of debris around the stylus. This detracts from print quality and necessitates frequent shutdown of the printer for cleaning as noted in U.S. Pat. No. 4,217,596. Because of the disadvantages of silicon dioxide, an alternative additive is suggested in U.S. Pat. No. 4,217,596 in the form of a combustible organic matte-causing substance, preferably polystyrene or polyethylene. The use of an organic, combustible matte-producing additive has the advantage over silicon oxide that practically no deposits will occur on the writing electrodes. Unlike silicon oxide, the organic matte-causing additive is burnt off upon recording. The result is very little, if any, residue around the electrodes. But organic matte-producing additives have the disadvantage of producing a diminished contrast effect. Other illustrative patents of the prior art include U.S. Pat. Nos. 2,833,677; 3,657,721; 3,861,952; and 4,024,546.
Accordingly, it is an object of the present invention to provide improved contrast in electrosensitive recording materials. A related object is to improve the contrast between the recorded information and the metallic outer surface of the recording material.
Another important object of the invention is to reduce the wear on the recording instrumentalities used with electrosensitive materials. A related object is to reduce stylus wear and also the buildup and retention of debris deposits, particularly those produced when the stylus comes into contact with the recording medium.
It is a further object of the invention to provide economical electrosensitive recording media having an array of desirable physical characteristics, including: printability, strength, flexibility, and reduced debris-causing characteristics.